Nanostructures have been extensively explored for use in gas/chemical/biological sensors, active and passive components for electronic devices, and many other applications. However, synthesis of nanostructures typically requires high temperatures and vacuum environments. Furthermore, most applications involving nanostructures require well-aligned patterns and/or micro arrays. Fabrication of such patterns and micro/nano patterned films also currently require a clean room environment and involve several lithography steps.
For example, a conventional patterned nanostructure-on-substrate fabrication method involves first vacuum filtration of a solution of nanostructured materials with filter paper so that the nanostructures are left on the filter paper. A planar stamp is then brought into conformal contact with the nanostructures on the filter paper so that the nanostructures on the filter paper are transferred to the planar stamp. The planar stamp having the nanostructures is then brought into conformal contact with a desired substrate to transfer the nanostructures from the planar stamp onto the desired substrate. A photo resist pattern is then formed on the nanostructures on the substrate using a photolithography process. Nanostructures not masked by the photo resist pattern are then etched away by a dry or wet etching process. The photo resist pattern is then removed from the nanostructures. Device and circuitry fabrication can then take place using the substrate carrying the patterned nanostructures.
In another conventional fabrication method, instead of using a planar stamp, a patterned stamp is provided to transfer the nanostructures from the filter paper to the desired substrate so that only a pattern of nanostructures is removed from the filter paper and transferred onto the substrate. Although photolithography is not required on the nanostructures after their transfer onto the substrate, photolithography is still required to form the pattern on the patterned stamp. Making the patterned stamp involves first fabricating a master mould. The master mould may be of silicon and made by developing a photo resist pattern on a surface of a silicon substrate using a standard photolithography process. The silicon substrate is then etched with the photo resist pattern acting as a mask, followed by removal of the photo resist mask from the silicon substrate to form a patterned silicon mould. The patterned silicon mould then undergoes surface treatment to facilitate stamp removal. Soft stamp material such as a polydimethylsiloxane (PDMS) is then poured or spin coated in liquid form onto the master mould to form the patterned stamp. Alternatively, metal or polymer moulds may be used, requiring processes such as precision cutting, grinding and polishing to achieve the desired pattern. Such processes are time consuming and labour intensive.